Shogo Yahagi, an 18 year old, is racing his bike at top speed through the morning traffic of mid 1980's Tokyo. A motorcycle cop is on his tail, sirens blazing, but he manages to ditch him. In the process of escaping the law, he turns up a walkway and almost crashes into a pedestrian, Yui Tananaka. He immediately apologises and starts to pick up the items which have fallen out of her bag. But she's not having any of it and gives him a serve for riding on the sidewalk. She runs off in a huff complaining that she'll be late, but Shogo rides up to her and offers a lift before she gets into the taxi she has just hailed down. She grudgingly takes up his offer and in no time she's at her destination. Shogo is interested in her, and decides to ask for her phone number. Yui is also a little interested in him as well and taunts him for a while, but eventually she relents and tells him her phone number at work. This has made Shogo's day, and he speeds off through Tokyo's streets. Shogo meets up with his friends, Hiroki Mori (known just as Mori to his friends), and two girls, Mai Yumekanou and Tomomi Murashita. The four of them have a fun filled day in Shibuya which doesn't end until the evening.

Later that night, Shogo meets his friend, Shinji Nakagawa, in an underground parking lot. He is a test rider for a new bike which he has brought from the company's garage. Shogo is puzzled but very interested by the bike, as he has never seen anything like it before. Shinji tells him that the bike is a Bahamut and can tops speeds of 320 kph. But they are soon interrupted by a man called BD, and two other men in suits. They try to force Shinji to come with them, but he is very suspicious as the company's security aren't armed like they are. Shogo switches off the lights and escapes with the test bike, while Shinji attempts to escape on Shogo's bike, but is killed. Shogo takes the bike to a bike shop he frequents, owned by a man named Coco. There Mori and Shogo's other biker friend, Shigeru Tomota, repaint the bike red in an attempt to disguise it. All of them suggest to Shogo that he should dump the bike, but he says that he can't because he doesn't know what they might do to him. Later Shogo discovers that the agents have staked out his flat, and that the company is telling everyone that Shinji has gone to America to study.

Shogo decides to take matters into his own hands, and plans to call up popular idol Eve Tokimatsuri on her live TV show, "Only You", to make the bike public. He manages to get Yui's home number from her workplace, but is rather surprised and a little embarrassed to find that Mai and Tomomi live in the same flat with her. He quickly tells Yui to watch "Only You", and hangs up. The girls watch the program and Shinji is the first caller. But as soon as Shogo says the name of the bike, "Bahamut Six", the screen goes blank and Eve soon returns with another caller. Yui, Mai and Tomomi wonder what happened to him. Meanwhile Shogo is still talking to Eve live on the air. He asks her if he can look into what happened to Shinji and also if he can bring the bike to the studio so an expert can look at it. She agrees, and he sets off for he studio.

On the way, several vehicles trap Shogo and the bike in what seems to be an accident. The drivers jump out of their vehicles to see if he's OK, but soon jump on him and try to pull him off the bike. Shogo realises that they're after him and the bike, and he manages to shake them off and escape, but not before ramming the bike trough several vehicles and a shop. He flees to the highway, and manages to take out two more agents on bikes in the process. On the highway, more bikes appear, this time looking more militaristic. They try to capture him using wires which launch from the bike and force him into the back of a truck, but they fail. Much to Shogo's surprise, one of the bikes transforms into a robot on the back of one of the trucks. The robot tries to capture him with a net, but Shogo's bike suddenly and unexpectedly transforms into a robot as well. In the resulting chaos, the truck smashes into the safety wall and explodes. Shogo and his robot is thrown clear of the highway onto a playground, where the robot transforms back into a bike. Shogo is amazed, but extremely happy.

Shogo calls Yui and asks if he can use her garage to hide the bike. Yui tells him that his call was cut off on Eve's show. Shogo is confused as he talked with her live on air for several minutes. Later he takes Yui to a park were he explains to her about the bike. Shogo explains that the reason he has surrendered the bike is because he wants revenge for his dead friend Shinji, but also that he doesn't mind the thrill of it all. That night Shogo tries to ask her out, but she tells him that she has to work on a TV show as a dancer. After the taping, she brushes him off for the producer, who takes her to a sleazy motel. Shogo is upset at this, and follows her with his bike, using the instruments contained within it to eavesdrop on her conversations with the producer. He finds which room they're in and realises that she is planning to sleep with the producer. He transforms the bike into the robot and crashes into the room, practically destroying it, and takes Yui. They drive off into the night, but though she seems rather surprised by the robot, she's not at all unhappy about what's happened. She laughs at the situation, but Shogo slaps her. He's angry at her for doing something like that, and she's angry at him for losing her chance at getting a leading part in one of the producer's productions. She walks off and tells him to leave her alone.

The next at Shogo's workplace, McDonalds, Tomomi proposes that they make a movie together with him the lead, using his bike of course. Though he initially says it'd be too dangerous to use the bike, he soon agrees, even though Yui is to play along side of him as the heroine. Shogo and Tomomi head off on the bike to scout for locations, but soon a motorcycle cop is on their tail. Shogo attempts to shake him off as they enter a tunnel. Tomomi spots an exit off the freeway to escape down. As the bike enters it, the barricades on the road open to let it through. The motorcycle cop continues through the main tunnel, oblivious to the fact Shogo and Tomomi are no longer on the freeway. Suddenly the section of road they're on moves downwards. It seems they are in some sort of goods elevator. The doors open to reveal a large open space with city, both on the top of roof and on the floor, with a large structure connecting the two cities filled with light coming from the middle of it. The cities seem to have been abandoned long ago, but people seem to be in the middle structure. Shogo switches on the eavesdropping gear on his bike and hears BD talking. He learns from his conversation with another man that Bahamut, the large structure, is actually a computer that controls his world and his bike is a terminal that is able to talk with the computer. Shogo realises that the situation has become more dangerous and suggests that Tomomi go back to the surface while he investigates the city a bit more. She waves him off, more excited about the fact she's found a prefect location for her film, rather than being concerned about what she has just learnt.

Shogo rides around the city and discovers another elevator that should lead to the middle of the Bahamut. Upon exiting he is attacked by several robots, and in the course of the fighting, ends up falling through a hole that was blasted in a floor into what looks like outer space. There seems to be debris for kilometres around, like some space war had been fought there. BD, who is fighting him in a robot, initially tries to kill him, but Shogo fights back and damages his robot. A truce is negotiated between the two when BD attempts to capture Shogo with grappling wire. Back inside BD tells Shogo that they are actually living inside a spaceship being controlled by a computer, and that very few people on the ship know the truth. The computer has fabricated their entire world to look like 1980's Japan. In reality at least five centuries have passed since the 20th century. BD takes Shogo to an airfield where fighters are launching into space to defend the spacecraft they live on. He explains that to try and defend themselves against an impending attack by a large object, named the Dezalg which is headed their way, they have to crack seven layers of protection in the Bahamut to stop it having any influence over the ship. Shogo's bike, the Garland, was to play a big part in final process of controlling the computer. BD warns Shogo that if he doesn't hand over the bike, he will kill him. Shogo is angered at this, and fires at BD, nicking his hair. He then angrily jumps over BD in the Garland and races out of the complex.

Tomomi calls a production meeting for her film. She describes the plot; two teenagers in a fabricated world controlled by a computer are threatened when they discover the truth. There's a dark cloud hanging over the room as Shogo and Yui are hardly talking to each other, and Shogo is rather depressed and feels helpless after the events of the last couple of days. Before he leaves, he suggests to Tomomi that she should change the story to include the fact that the fabricated world is actually on a spaceship. The filming of the movie begins the next day. Yui, feeling a little concerned for Shogo, tells him about Mai's new job singing back up for Eve Tokimatsuri. At a TV taping, Eve didn't show up, in fact hardly anyone has seen her in person. She's never even had a live concert. The penny drops for Shogo. He heads to the TV studio that night to confirm his suspicions. Disguised as a delivery boy, he sneaks into the studio where Eve is recording. Instead of finding her, he sees banks and banks of TV screens set up with hundreds of cables everywhere. The image of Eve grinds to a halt. Shogo then hears the staff talking about how the computer creates Eve's songs, and realises that Eve is not a real person, but computer generated.

Completely incensed at the deception, Shogo goes on a rampage in the Garland, kicking and destroying a police car that was chasing him. He then calls BD to tell him that he has met the real Eve, but BD seems blasé about it all and tells him that Eve is Bahamut's work, not the military's. Shogo vows to expose the whole thing, but BD reminds him what happened last time he tried to show the Garland on TV. Meanwhile the military have cracked the Bahamut's last level of protection and almost have complete control over it. But the Dezalg is heading towards them fast.

The following day, Eve contacts Shogo on the Garland. Eve tells Shogo that she is a part of a program called EVE created by humans, who several hundreds of years ago destroyed planet Earth in a war. They left the Earth searching for new planets to inhabit, but wars continued on in space. Another war between two of the ships is about to take place, which will mean the end of the world they live in. Eve was created to protect the inhabitants from the war, but now she is being disabled. She needs his help desperately. Shogo asks she chose the late 20th century as a time for the population to live in. She replies that it was the most peaceful time in history. The screen goes blank as Eve makes one more last plea for help to Shogo. Shogo is completely stunned at what he has heard.

Shogo asks Yui out, but she can't seem to get any sense out of him. He seems very depressed and angry. He asks if he can sleep with her, but then walks out after she questions him. Yui follows him, but all he says is that he doesn't know what he should do and he eventually breaks down. Yui is extremely puzzled and worried at his behaviour, but she relents and goes to a love motel with him. They make love and later Shogo explains everything he's learnt to her. Meanwhile during a TV performance, Eve suddenly turn to camera and pleads for help saying that she's about to be killed. The screen goes blank and a news bulletin appears. One of Japan's fuel tankers was bombed by a foreign power. In reality, the military has gained control of the Bahamut, and is preparing it's citizens for war. But BD has another plan and puts it into motion. He takes over the government in a coup d'état, which effectively means he has control over the entire spaceship. BD calls Eigen Yumekanou, to tell him that the coup was successful. Eigen, Mai's father, is a successful businessman, mostly in dealing arms, and has funded BD's actions to take over the government.

Media reports tell the population that a war has broken out. Meanwhile the war outside the spacecraft has already started. But it's a battle that's being lost. They are out classed and out numbered. Despite the chaos in the city, production on Tomomi's film continues. As a scene is filmed with Yui and Shogo in the city centre, Eve appears on one of the large screens above disrupting the cast and crew. Eve is now being used as a military tool, spruiking for applicants to join the war. Later at Coco's bike shop, Coco and Shogo see Mori and Shigeru on a news report signing up as volunteer soldiers. Coco is angry that they'd do something that stupid. Late at night, Tomomi is busy editing her film in her room while the others are out. But BD's men kill her in cold blood and take all the film of the Garland. Yui, Mai and Shogo later find her body. Shogo is enraged and takes off to find BD. Mai's father calls asks her to return home since war has broken out. As Mai is driven away, Yui hopes that Shogo will return to her.

Shogo speeds towards the Bahamut and plans to destroy it with the Garland. BD's men give chase and attempt to kill him, but most are shot down by Shogo. He tries to fire his gun at Bahamut, but the gun is spent. More robots come after Shogo, and despite having no weapons, he manages to take one out and grabs it's gun. Another battle ensues, with the military losing out to Shogo. That is until BD shows up in his robot. Shogo fires wildly until he is out of ammunition. BD then attacks his Garland until both Shogo and the robot itself are completely beat up and unable to move. BD throws the Garland and Shogo on the elevator which takes them to the surface. Later Shogo is awakened to Eve's singing, which is coming from a video being played on the Garland's monitor, seemingly the EVE program's final desperate gesture to make contact with him. He opens the cockpit and struggles out into the deserted early morning streets. As blood drips almost non stop from his wounds onto the sidewalk, he recalls what has happened to him over the last several days. But now the only thing which is keeping him going is his thoughts of Yui.